The present invention relates to a design for an electrochemical transducer for use in various sensors, such as seismometers and other motion detectors. In addition, the present invention is concerned with a method for fabricating such a device.
Electrochemical transducer design is well known in the prior art and has been used primarily in seismometers, and other motion detectors. Typically, an electrochemical transducer operates by measuring the motion of an electrolytic fluid. To do this an electrochemical transducer is usually placed in a channel of a motion sensor filled with a specially prepared electrolytic solution, as shown in FIG. 1. A DC offset is then applied between the anodes causing an ionic flow, thus rapidly reducing the electric field within the bulk of the electrolytic fluid and resulting in a concentration gradient. When the motion detector experiences an acceleration, the electrolytic fluid experiences a motion relative to the channel which is communicated to the electrochemical transducer and which entrains ions and causes an additional charge transfer between the electrodes. This charge transfer is measured and interpreted as acceleration being detected.
As shown in FIG. 1, current electrochemical transducer 99 designs typically consist of four platinum electrodes (two anodes 100, two cathodes 102) separated by thin, microporous ceramic spacers 104, all of which are held together via a ceramic housing 106. The transducer is then embedded into a sensor housing which is then mounted into a motion detector 110, such as a seismometer, which includes a channel 112 filled with a specially prepared electrolytic solution 114. Two anode leads 116 and two cathode leads 118 are typically provided for communication with anodes 100 and cathodes 102, respectively. The transducer is typically placed within the channel 112 and hence is immersed within the electrolytic solution 114. In addition, the sensor housing is typically constructed out of a stable polymer (such as polysulfone) or a ceramic similar to that of the transducer. This existing design is capable of performing under relatively severe limitations placed on it by its operating environment. Among the limitations placed on this device is that all components of the device must be impervious to the aggressive chemical nature of the electrolytic solution.
In addition, because even the slightest movement of the electrodes under the influence of the electrolytic flow would cause a significant degradation of transducer performance, the transducer geometry must be extremely stable. This stability acts to minimize noise and distortion and works to ensure an accurate measurement.
To prevent cracks from forming in the ceramic components during the baking process, all ceramic parts must be prepared from the same original raw composition and very stringent preparation requirements must be imposed upon the temperature regime inside the furnace. All temperature gradients across the assembly must be reduced to near zero during the heating and the cooling process. This is time consuming and, even with the best precautions, the production yield is usually low, making mass production exceedingly expensive and impractical.
Lastly, because this geometric stability must remain over the operating temperature range and the life of the instrument, all of the components must be rigidly mounted and all components must have comparable temperature expansion coefficients.
However, this transducer has several major shortcomings related to its design and fabrication process. One such shortcoming is the preparation of the microscopically thin ceramic spacers. This preparation process is a labor-intensive and delicate process which has a very low yield.
Another problem associated with the baking process is that the ceramic shrinks during cooling which can result in warped electrode assemblies and non-uniform pore patterns. This leads to a micro-turbulent flow when the electrolyte moves through the transducer in response to ground motion and thus causes a non-linear transducer output which becomes more pronounced with increased electrode assembly size. In addition, this shrinking may cause the spacer thickness to be non-uniform, creating additional signal distortion.
These limitations place a practical limit on the size of the transducers to about six millimeters in diameter and because an electrochemical transducer""s signal-to-noise ratio is proportional to the linear dimension of the transducer, it is desirable to have electrochemical transducers larger then current electrochemical transducer sizes. However, this is impractical because larger ceramic pieces are more susceptible to thermal gradients across their dimensions during the baking and cooling process, thus they are more susceptible to cracking. Because larger ceramic pieces tend to demonstrate more pronounced dimensional irregularities than do smaller ceramic pieces, larger electrochemical transducers are difficult and more costly to produce than smaller electrochemical transducers.
Unfortunately, because the majority of these problems are created during the baking process, these problems only become apparent after the completion of the heating and cooling cycle, making mass commercial production costly and yield predictability highly unreliable.
The need remains for an electrochemical transducer design which incorporates or exceeds performance characteristics of current electrochemical transducer designs, yet is relatively simple and inexpensive to produce. In addition, the need remains for an electrochemical transducer design and fabrication method that allows larger electrochemical transducers to be produced with a much more predictable yield.
An embodiment of the invention is an electrochemical transducer which comprises: two housing plates, each of the housing plates being constructed of a polymer material and wherein each of the housing plates include an inner side, an outer side and a plurality of channels through the housing plates so as to communicate the inner side with the outer side; two anode electrodes, the anode electrodes disposed so as to be sandwiched between the housing plates; two cathode electrodes, the cathode electrodes disposed so as to be sandwiched between the anode electrodes; and three porous insulating layers, the insulating layers being constructed of a polymer mesh and wherein each of the insulating layers is disposed so as to separate each of the anode electrodes from the cathode electrodes and each of the cathode electrodes from each other, while permitting the flow of an electrolyte between them.
Another embodiment of the invention is a method for fabricating an electrochemical transducer comprising: obtaining two anode electrodes, wherein each of the anode electrodes has an anode lead; obtaining two cathode electrodes, wherein each of the cathode electrodes has a cathode lead; obtaining three insulating layers, wherein each of the insulating layers are constructed out of a polymer mesh having insulating and porous properties; obtaining two housing plates, the housing plates being constructed of a polymer material and having an outer edge and a plurality of channels so as to allow communication through the housing plates; arranging the anode electrodes, the cathode electrodes and the insulating layers so as to be parallel with each other, wherein the cathode electrodes are disposed between the anode electrodes and wherein one of the insulating layers is disposed between the cathode electrodes and between each of the anode electrodes and the cathode electrodes so as to form a core subassembly; arranging the housing plates so as to be parallel with each other; positioning the core subassembly between the housing plates such that the core subassembly is communicated with the plurality of channels; compressing the housing plates together so as to supportingly and non-movably hold the core subassembly between the housing plates; and securing the housing plates together using a plate securing means so as to create a transducer.